6500 CatOs command sh port mac util and MRTG/SNMP values

Hi, i'm confused about the 5 minutes average values from the 6500 CatOs
command SHOW PORT MAC UTILIZATION (times 8 because of octets) and the values
gathered by MRTG/SNMP with default config (cfgmaker and bits option).

Does anyone know how the values, shown with sh port mac util, are
calculated? They do not seem to match the values calculated by MRTG/SNMP.

When I calculate the average over aprox. 5 minutes (Transmit2-Transmit1)*8
(octets) /300 (seconds), with the values from the command sh port mac, it
matches MRTG again. So MRTG seems to calculate the right values...

Search on cisco.com on the catos command show port mac utilization does not
give any answers.

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"H.U.A. Koers" <> wrote in message
news:c97172$hcm$...
> Hi, i'm confused about the 5 minutes average values from the 6500 CatOs
> command SHOW PORT MAC UTILIZATION (times 8 because of octets) and the
values
> gathered by MRTG/SNMP with default config (cfgmaker and bits option).
>
> Does anyone know how the values, shown with sh port mac util, are
> calculated? They do not seem to match the values calculated by MRTG/SNMP.
>
> When I calculate the average over aprox. 5 minutes (Transmit2-Transmit1)*8
> (octets) /300 (seconds), with the values from the command sh port mac, it
> matches MRTG again. So MRTG seems to calculate the right values...
>
> Search on cisco.com on the catos command show port mac utilization does
not
> give any answers.
>
> TIA, Arjen
>

Does the 6500 show more than 100 Mb/s being used on the port? If so, you'll
need to tell MRTG to use 64-bit counters. You do this by telling MRTG to
use SNMPv2c.

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Correct! Normal counters do reset too often to get satisfied results, when I
use the HC / SNMPv2 option ::::2 behind every interface) results become
more visible / clear. Can use the snmp version option in cfgmaker to tell
MRTG to always use SNMPv2

Thanks Tax!

"Tax Johnson" <> wrote in message
news:6%Qtc.26653$-kc.rr.com...
> "H.U.A. Koers" <> wrote in message
> news:c97172$hcm$...
> > Hi, i'm confused about the 5 minutes average values from the 6500 CatOs
> > command SHOW PORT MAC UTILIZATION (times 8 because of octets) and the
> values
> > gathered by MRTG/SNMP with default config (cfgmaker and bits option).
> >
> > Does anyone know how the values, shown with sh port mac util, are
> > calculated? They do not seem to match the values calculated by
MRTG/SNMP.
> >
> > When I calculate the average over aprox. 5 minutes
(Transmit2-Transmit1)*8
> > (octets) /300 (seconds), with the values from the command sh port mac,
it
> > matches MRTG again. So MRTG seems to calculate the right values...
> >
> > Search on cisco.com on the catos command show port mac utilization does
> not
> > give any answers.
> >
> > TIA, Arjen
> >
>
> Does the 6500 show more than 100 Mb/s being used on the port? If so,
you'll
> need to tell MRTG to use 64-bit counters. You do this by telling MRTG to
> use SNMPv2c.
>
> http://people.ee.ethz.ch/~oetiker/webtools/mrtg/mrtg-reference.html
>
>

"H.U.A. Koers" <> wrote
> Correct! Normal counters do reset too often to get satisfied results, when I
> use the HC / SNMPv2 option ::::2 behind every interface) results become
> more visible / clear. Can use the snmp version option in cfgmaker to tell
> MRTG to always use SNMPv2
> > > Hi, i'm confused about the 5 minutes average values from the 6500 CatOs
> > > command SHOW PORT MAC UTILIZATION (times 8 because of octets) and the
> values
> > > gathered by MRTG/SNMP with default config (cfgmaker and bits option).
> > >
> > > Does anyone know how the values, shown with sh port mac util, are
> > > calculated? They do not seem to match the values calculated by
> MRTG/SNMP.
> > >
> > > When I calculate the average over aprox. 5 minutes
> (Transmit2-Transmit1)*8
> > > (octets) /300 (seconds), with the values from the command sh port mac,
> it
> > > matches MRTG again. So MRTG seems to calculate the right values...

I agree with the counter overflow issue described earlier,
however there is another issue.

The 5 min (or whatever you set the "load interval" to value is
NOT a 5 min (or "load I..) average.

It is IIRC an Exponential Weighted average with a Time Constant
of 5 (or whatever) minutes.

In my experience with the default 5 min "load interval", if the
actual load is changed from say 0% to say 50% suddenly,
the displayed load changes for between 15 and 20 minutes.

Thanks for that info, IMO the calculated "average" has indeed sort of an
exponential factor. When a link suddenly dies, the average smoothly fades
away instead of just becoming 0. The same is with spikes in the network.

Arjen

"AnyBody43" <> wrote in message
news:...
> "H.U.A. Koers" <> wrote
> > Correct! Normal counters do reset too often to get satisfied results,
when I
> > use the HC / SNMPv2 option ::::2 behind every interface) results
become
> > more visible / clear. Can use the snmp version option in cfgmaker to
tell
> > MRTG to always use SNMPv2
>
> > > > Hi, i'm confused about the 5 minutes average values from the 6500
CatOs
> > > > command SHOW PORT MAC UTILIZATION (times 8 because of octets) and
the
> > values
> > > > gathered by MRTG/SNMP with default config (cfgmaker and bits
option).
> > > >
> > > > Does anyone know how the values, shown with sh port mac util, are
> > > > calculated? They do not seem to match the values calculated by
> > MRTG/SNMP.
> > > >
> > > > When I calculate the average over aprox. 5 minutes
> > (Transmit2-Transmit1)*8
> > > > (octets) /300 (seconds), with the values from the command sh port
mac,
> > it
> > > > matches MRTG again. So MRTG seems to calculate the right values...
>
> I agree with the counter overflow issue described earlier,
> however there is another issue.
>
> The 5 min (or whatever you set the "load interval" to value is
> NOT a 5 min (or "load I..) average.
>
> It is IIRC an Exponential Weighted average with a Time Constant
> of 5 (or whatever) minutes.
>
> In my experience with the default 5 min "load interval", if the
> actual load is changed from say 0% to say 50% suddenly,
> the displayed load changes for between 15 and 20 minutes.
>
> The exact behaviour is described in:
> http://www.cisco.com/warp/public/66/3.html

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